SOCIETY OP THE UNIVERSITY OF ABERDEEN. 179 



completed. They may, however, persist in adult life (Fig. 1). In 

 these cases they do not close until the other sutures of the skull be- 

 come obliterated. 1 Now, since these sutures normally close before 

 the maximum size of the brain is reached, it would appear that the 

 determining cause of their consolidation cannot be the mere cessation 

 of an expanding pressure from within, more especially as in some 

 cases of hydrocephalus the metopic suture becomes closed at the 

 usual age, viz., before the sixth year. In the normal condition, it is, 

 however, just possible that since the pressure of the growing brain is 

 not absolutely equal in all directions, and the falx cerebri is attached 

 internally along the line of the metopic suture, that an outward force 

 exerted on the lateral margins of each half of the frontal bone might 

 cause an inward movement of the mesial borders, each half of the 

 bone rotating round a vertical axis passing through or near the 

 external angular process. 



Now we occasionally meet with skulls in which the frontal region 

 is extremely narrow, and comes to a point in front, whereas the skull 

 behind is abnormally wide. The outline of such skulls when viewed 

 from above is triangular, the apex of the triangle being directed for- 

 ward. These skulls are called trigonocephalic (Plate XL, Fig. 3), and 

 it is usually believed that the condition is due to premature closure of 

 the metopic suture, which has prevented the expansion of the skull in 

 the frontal region, and that the increased width in the parietal region 

 is compensatory. Premature union of the two halves of the frontal 

 bone, however, is not always followed by trigonocephaly, for in a 

 specimen in the Anatomical Museum at Cambridge, which was shown 

 me by Professor Macalister, though the two halves of the frontal 

 bone of a foetal skull were united, the suture being completely obli- 

 terated, there were no signs of trigonocephaly, though there is a 



1 The persistence of the metopic suture in aged subjects is shown in several speci- 

 mens in the Museum of the Eoyal College of Surgeons, England, and a case is recorded 

 by Simon, in which, in a man aged seventy-five, though all the other sutures of the skull 

 were closed, the metopic had persisted (" Ueber die i'orsistenz der Stirnnaht," Dr. 

 Theodor Simon, Vircliow's Archiv, Iviii., s. 572). 



